[ntp:questions] how long does it take ntpd to sync up

Chris Albertson albertson.chris at gmail.com
Sat Aug 27 18:15:11 UTC 2011


On Sat, Aug 27, 2011 at 9:49 AM, C BlacK <rblak at non.net> wrote:

> I read somewhere that it takes an ntpd 24 hours to truly sync up to a
> stratum 2 master.
>
>
Use some logic.   Assume you want to set a mechanical clock's speed by
moving the "slow/fast" lever and you can see the time only to the nearest
second by eye.  If you want the clock to loose/gain one second per day then
it will take you one day (at best) to adjust the time as it would take that
long to detect an error.   It you want to adjust the rate such that it only
gains one second per month it would take a month before you'd know if you
got it right.  You have to remember that NTP works be adjusting the rate,
faster or slower and tried hard to never "jump" the time.   The only why for
anyone to know if the rate is right is to wait, greater accuracy requires
longer a wait.

NTP works kind of like this.  Small errors take a long time to detect and
smaller errors take even longer to detect.  So up to a point NTP's error
gets smaller the longer you wait.  The details depend on your Internet
connection and the distance to the server(s).  For most people a "few" hours
gets you "close" and you are almost as good as you will be after a half day.
   After 24 hours improvement is unlikely.

So the conservative answer is "24 hours" but for most practical purposes you
are "good enough for file system time stamps and the like" after 1 or 2
hours.



-- 

Chris Albertson
Redondo Beach, California



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